Correction of Class II malocclusion with Class II elastics: A systematic review

data were independently abstracted by 3 investigators (R.S., T.M.F.F., and N.C.C.B.) and then discussed to reach a common agreement. Ideally, we intended to compare the effects of elastics with other Class II treatment modalities; therefore, a meta-analysis would be recommended. However, because of the differences in the articles in the elastics only category and the different types of fixed functional appliances in the comparative studies category, a metaanalysis was not possible. 

RESULTS 

In total, 417 articles were retrieved. Starting from PubMed, a comparison between bases was made to eliminate duplicated articles. As a result, 162 articles were retrieved from these databases. Among the 162 retrieved articles, 11 dealt with clinical studies of Class II elastics applied in Class II malocclusion correction. When we separated the articles based on the type of study, 4 articles fell into the category of elastics only, with Class II elastics used to treat Class II malocclusions without other treatment appliances or protocol, and 7 were comparative studies in which primarily Class II elastics were compared with another appliance or protocol for Class II malocclusion treatment (Tables II and III). The most frequent ways of use of, and the main effects caused by, Class II elastics in Class II malocclusion treatment were evaluated in each retrieved and accepted article. Only 1 article described the elastic diameter used: 3/16 in.15 The forces applied were given in 5 articles (1-2,13,20 2.5,16 3.5,18 and 415 oz), and the mean force was 2.6 oz (73.7 g). The wire dimensions were described in only 2 articles; both applied Class II elastics on 0.016 3 0.022-in stainless steel wires15,18 in an 0.018-in slot bracket.15 The prescriptions were described in only 3 articles that required full-time wear.7,13,18 Duration of active treatment with Class II elastics was mentioned in only 1 article (8.5 months).18 One article found a tendency of predominantly skeletal effects consequent to the use of Class Elastics only For more consistent data on the true dentoalveolar effects produced by Class II elastics, only the articles in the elastics only category were analyzed. This was done to eliminate bias from comparisons of elastics with other appliances. Therefore, the effects could only have been due to the exclusive use of Class II elastics. Forward maxillary growth appeared to be restrained, and the maxillary molars did not move significantly. Conversely, forward growth of the mandible occurred, and the mandibular first molars moved 1.2 mm forward. The mandibular incisors were proclined.13,20 During the total treatment
period, overjet reduction was 5.8 mm. There were 18.9% of skeletal and 71.1% of dental changes. Overbite reduction in the total treatment period was
3.0 mm, and molar correction was 3.0 mm: the dental changes comprised 1.9 mm (63%) and the skeletal, 1.1 mm (37%). Mandibular growth exceeded maxillary growth by 1.1 mm. The lower anterior face height increased by an average of 5.0 mm.13 The occlusal plane angle increased during treatment but had a tendency to return to the original condition later.13,15,20,21 These combined effects contributed to correction of the Class II malocclusions. Hence, Class II elastics are effective in correcting Class II malocclusions, and their effects are mainly dentoalveolar. Soft-tissue effects were vaguely
mentioned by these articles, and few variables were dedicated to this subject. Only 2 articles evaluated these effects, reporting increases of upper and lower lip thicknesses of 0.7 and 1.2 mm, respectively,15 and a reduction of 1.48 of the Holdaway soft-tissue angle.20  

Comparative studies

The comparative studies in which Class II elastics were exclusively used and compared with another Class II treatment appliance produced the most interesting results. When Class II elastics were compared with the Fr€ankel function regulator, headgear,19 the cortical anchorage principle,11 and the Forsus appliance7 to correct Class II malocclusions, no differences were found in the changes produced by these approaches. In the short term, the Herbst appliance achieved greater skeletal changes than did Class II elastics. The Herbst appliance corrected the overjet with 51% of skeletal changes, whereas Class II elastics produced only 4% of skeletal correction. In the molar relationships, the Herbst achieved 66%, and Class II elastics achieved
10% of the skeletal correction. However, the authors suggested that, when the posttreatment time period is longer (2-3 years), the amount of natural growth increases, and this could mask the effects of the appliances, wiping out the effects of treatment and perhaps making the 2 groups comparable again.14 Comparison of the results between Class II elastics and the reciprocal mini-chincup appliance in Class II malocclusion treatment showed that overjet correction  resulted mainly from dentoalveolar changes with both devices, and molar correction was 87.36% dentoalveolar for the reciprocal mini-chincup appliance and 51.47% for Class II elastics.18 Both devices achieved a Class I molar relationship, with 4.5 mm of molar correction in the reciprocal mini-chincup group and only 2 mm for the Class II elastics group. Other skeletal and dental changes were similar in both groups. Summarizing the findings of the comparative studies showed that, on a long-term basis, there are no significant differences between the effects of Class II elastics
and other removable or fixed functional appliances in Class II malocclusion treatment.

DISCUSSION

The aim of this systematic review was to obtain every article on Class II elastics published in PubMed, Scopus, Web of Science, Embase, Medline, and Cochrane databases, and by hand searching. This sort of review reduces the tendency to favor 1 particular point of view and allows acquiring all data published in the most respected journals, indexed in these databases. From the 162 retrieved articles, only 11 met the final criteria and were selected for this review. With these data, we determined that sample descriptions and details in the use of Class II elastics have been omitted by most authors. Sample description such as mean age is important to understand the results obtained, and the sample size is important to be able to determine the validity of the results and conclusions. All 11 of the accepted articles described the subjects’ mean ages and the numbers of patients comprising
the samples. Conversely, only 3 articles described the Class II malocclusion occlusal severity in the samples; this allows a more precise evaluation of the occlusal effects of the elastics.7,16,20 Identification of the occlusal malocclusion severity is essential to characterize the sample, describe the treatment difficulty of the patients, and, most importantly, determine the best treatment approach.6 Additionally, only 6 articles described at least 1 aspect of Class II elastic use (Table IV).7,13,15,16,18,20 Consequent to the few articles that described these details, there are no significant data to be able to determine the most convenient protocols to correct Class II malocclusion with Class II elastics. For this reason, it can only be stated that the current literature suggests using light forces (average, 2.6 oz) obtained with a 3/16-in diameter elastic and a rectangular 0.016 3 0.022-in stainless steel archwire. Because Class II elastics heavily rely on patient compliance, full-time usage is recommended. Within an average period of 8.5 months, correction of the Class II discrepancy is usually obtained with predominant dentoalveolar effects (Tables II and III). Because malocclusion severity was specified in only 3 articles to be at least an end-to-end Class II malocclusion, it can be speculated that this is the treatment time to correct an end-to-end Class II malocclusion or less.7,16,20 Additionally, little attention has been given to the soft-tissue effects caused by this treatment modality. Therefore, research on this topic is necessary to determine the soft-tissue impact caused by Class II elastics used in Class II malocclusion treatment. Finally, because Class II malocclusions might result from combinations of dental and skeletal factors ranging from mild to severe, the effects described
here apply to general Class II malocclusions and not to specific types.1,2 Further investigations on each type are necessary.

Elastics only

Overall, the use of Class II elastics in Class II malocclusion correction produced primarily dentoalveolar effects (Tables II and III).13-16,18 These results seem to be reasonable because of the relatively light force applied (73.7 g)13,15,16,18,20 during a mean period of 8.5 months,18 with an average recommended use of 24 hours per day.7,13,18 Usually, skeletal changes are generally produced by appliances that apply heavier forces during longer periods of time.22-24 No study has emphasized any collateral effects produced by the elastics, as previously suggested.9-12 Therefore, Class II elastics are also a valuable tool that can be used either alone or with other appliances to correct Class II malocclusions, without significant side effects.

Comparative studies

Complementing the previous results, the comparative studies showed that the changes produced by Class II elastics are similar to those produced by functional appliances in the long term.16,17 In the short term, the Herbst appliance achieved greater skeletal changes than did Class II elastics.14 This difference is most probably because the Herbst appliance is fixed and therefore acts continuously for 24 hours a day, whereas the elastics act only when placed in position. Although elastics can be recommended to be used up to 24 hours per day, it is likely that patients use them only about half of the recommended time, as with functional appliances. 25 These studies have shown not only that Class II elastics are effective in correcting Class II malocclusions but also that the changes produced by these devices are similar to those of functional appliances. Consequently, Class II elastics are definitely an additional option to correct Class II malocclusions. However, most studies included in this systematic review were retrospective. Retrospective studies are not ideal, but, in the absence of stronger evidences, they can provide satisfactory information to guide our clinical
procedures.26-29 All age groups were included because age limitations would also decrease the number of suitable articles. By current standards, these can be serious limitations of the review. Therefore, for now, we must accept that these changes are the actual effects of Class II elastics in Class II malocclusion treatment, and that they are similar to those with either removable or fixed functional appliances, until future prospective randomized or controlled investigations can confirm them. Selection criteria of the studies were as restricted as possible to include fairly good investigations and the best studies on the topic. Increasing the criteria severity to require only randomized prospective or controlled studies would not have allowed inclusion of a single article. Scientific methodologies have improved in recent years; consequently, not many articles have a high quality level, based on current standards, for a specific subject.30 The use of Class II elastics in Class II malocclusion correction is a controversial issue, with much emphasis on their side effects.9-12 Therefore, to elucidate this issue, our intention in this systematic review was to show the level of evidence regarding the changes that
can be obtained with these devices and also how they compare with other Class II treatment modalities. Randomized clinical trials comparing Class II elastics with functional appliances in Class II malocclusion correction are necessary to provide more detailed information on the effects of these devices.

Clinical implications 

The belief that functional appliances have mainly skeletal effects, compared with Class II elastics, is not based on strong scientific evidence. Some authors have stated that little evidence supports the claim that functional appliances significantly affect mandibular growth, especially in the long term.31,32 Others have stated that the most significant treatment effects of functional appliances are restricted to dentoalveolar changes.16,33
The articles that we evaluated showed more similarities  than differences between these 2 treatment devices. After analysis of the accepted articles, it became clear that further research is needed to clarify the permanent skeletal effects of functional appliances in Class II malocclusion treatment.31 It seems that the well-known orthopedic effects34 produced by this treatment protocol do not last over the years.14,16,35 Because of these findings and based on this systematic review, it is possible to state that, in the long term, there are no relevant differences between treatment effects produced by functional appliances and Class II elastics, since both protocols have a predominance of dentoalveolar effects as an enduring result. Again, as previously stated, these results apply to Class II malocclusions in general and not to specific types. It was not our intention to defend the indiscriminate use of Class II elastics in Class II malocclusion treatment but only to elucidate that there is no strong evidence that they have mainly side effects, as previously suggested. 9-12 There is still a need for a detailed description of Class II elastics protocols of usage: eg, diameter, strength, prescription, appropriate wire, and periods of wear. The importance of overcorrection, active retention, and differential growth, which are relevant issues about the stability of the results, are sometimes disregarded by our scientific community.36 Although these are speculations, we can at least state that, on a long-term basis, Class II elastics have similar effects to other methods for Class II malocclusion treatment, such as fixed functional appliances, contrasting with the common belief that these appliances promote greater skeletal effects than do Class II elastics. This systematic review demonstrated that these differences are diminished by time.

CONCLUSIONS

Class II elastics are effective in correcting Class II malocclusions, and their effects are mainly dentoalveolar, including lingual tipping, retrusion, and extrusion of the maxillary incisors; labial tipping and intrusion of the mandibular incisors; and mesialization and extrusion of the mandibular molars. Little attention has been given to the soft-tissue effects of this treatment modality. These effects are similar on a long-term basis to those produced by functional appliances; this places these 2 methods close to each other when evaluating treatment effectiveness.